The latest generation of brushless electric motors have recently become available, and are characterized by having a specific power, that is to say a power-to-weight ratio, which is significantly higher than that of earlier electric motors. It would therefore be desirable to use these motors also in robotic applications. However, these motors run at much higher speeds than those that can be withstood by the recirculating ball screws normally used in robotics, and therefore it has been impossible to use the full potential of these new motors hitherto. Consequently, there is a need to provide a linear drive device which is able to operate at much higher speeds than those permitted by recirculating ball screws. There are existing alternative solutions with better performances than recirculating ball screws, such as roller screws or rolling ring screws, but these suffer from a number of drawbacks. Roller screws are very costly because of the complex shape of their components. The currently known rolling ring screws have at least one of the two following drawbacks: the contact between the threaded shaft and the rolling rings is a point contact, which limits the transmissible force, and the relative movement of the threaded shaft with respect to the rolling rings is not a perfect rolling movement but has a degree of slip, thus increasing the frictional losses and consequently reducing the mechanical efficiency. Examples of rolling ring screws are known from U.S. Pat. Nos. 4,856,356 and 6,244,125.
A linear drive mechanism according to the preamble of independent claim 1 is known from EP 0 122 596.